A printing apparatus such as multi function peripheral (MFP) or the like forms an image on a sheet based on image data received from an external apparatus.
A printing apparatus of one type forms an image on a sheet with a decolorable material. The image formed with the decolorable material can be erased when the printed image is no longer needed. The decolorable material is usually decolored when heated to a high temperature. Since the sheet from which the image has been erased can be used for printing again, using the decolorable material leads to reduction of sheets and further to conservation of the environment.
However, a document having images formed with the decolorable material may be falsified, for example, by erasing partially or completely the images formed with the decolorable material and replacing them with different images. It would be desirable if such a risk can be minimized.